Helicopters employ a tail rotor to counteract the torque exerted by the main rotor and thereby provide stability and direction control. The tail rotor is driven by a tail rotor driveshaft. Because the helicopter tail boom cannot be perfectly ridged, the tail rotor driveshaft is typically designed to be supported by bearings so that some movement can occur. Typically, the driveshaft is supported by hanger bearings (also referred to as tail rotor driveshaft support bearings).
FIG. 1 shows an exploded view of an exemplary prior art tail rotor driveshaft 1. The circled items in FIG. 1 are exemplary prior art pieces of a hanger bearing support system 2. Although not all hanger bearing support systems are designed alike, in general a hanger bearing support system has two functions: 1) to support the tail rotor driveshaft and 2) to maintain the hanger bearing alignment with the tail boom. As shown in prior art FIG. 2, a hanger bearing support system 20 is supporting a driveshaft 10 of a helicopter and is securely attached to a tail boom 30 of the helicopter by a hanger bearing system bracket 40.
As transmission of torque through the tail rotor driveshaft is necessary for the operation of the helicopter, monitoring the degradation and wear of the hanger bearing assists operators and maintenance personnel with maintaining a strong connection between the components of the tail rotor driveshaft. To that end, helicopters often include health and usage monitoring systems (HUMS), which use sensors and other sources of data on a helicopter to keep track of and determine the status and condition of various aspects of the helicopter. HUMS can monitor hanger bearings for degradation and wear, but in order to properly monitor a hanger bearing for degradation and wear, a sensor or monitoring device needs to be able to detect the vibrations associated with the hanger bearing and the tail rotor shaft assembly. This requires that the monitoring device be attached, generally in very close proximity, to the hanger bearing so as to ensure a good transfer path from those vibrations to the monitoring device.
Monitoring devices for detecting these vibrations that are installed proximate hanger bearings typically include accelerometers, which can measure information from which features can be extracted that are characteristic of hanger bearing faults. Additionally, accelerometers can measure features associated with shaft damage, such as imbalance, a bent shaft, or a failure of the shaft coupling.
However, installing monitoring devices on or near hanger bearings can pose challenges. For many aircraft, the hanger bearing is relatively small and therefore mounting a monitoring device proximate the hanger bearing is difficult. As shown in the prior art hanger bearing support system 20 in FIG. 2, for example, the hanger bearing mounting bracket 40 includes ¼ inch bolts (50a and 50b) that are spaced about 2.5 inches apart. Further, as can been seen, there is little clearance between the tail boom 30 and the driveshaft 10 where a hanger bearing monitor can be properly and securely mounted given the size and connection requirements of such monitoring devices. For current digital sensors (such as the sensor 60 shown in prior art FIG. 3), for example, the sensor is bused, which requires an interconnect (such as of the interconnect 70 shown in prior art FIG. 4) with a bus/power cable. As is evident, the size, shape and configuration of digital sensors do not make them conducive for mounting to a hanger bearing. Moreover, a typical interconnect 70 includes two mounting apertures 80 (80a and 80b in prior art FIG. 4). For aviation and other high vibration installations, the two mounting apertures 80 help ensure that the interconnect 70 does not loosen or turn over time; however, the downside of this design is that it necessitates drilling two holes in the tail boom 30 structure to mount the interconnect 70, which adds cost and time to mounting.
Therefore, there is a need for a hanger bearing monitor that can be properly and securely mounted to a hanger bearing mounting bracket on a tail boom of a helicopter in a cost effective manner and that does not add much extra weight to the system.